The exit polls from Michigan may or may not have been skewed somewhat by mischief-making Democrats who turned out to vote for Rick Santorum. But even allowing for some irregularities, they offer a useful snapshot of the GOP candidates’ relative strengths. Here are Decoder’s top five takeaways:

Ground game matters: Michigan voters who decided “in the last few days” voted for Santorum over Romney, by a notable margin of 18 percent. But voters who said they decided on Election Day went for Romney, by 7 percent. The Romney campaign clearly outperformed Santorum in getting its voters to the polls.

Santorum really, really wishes he hadn’t said that the historic speech about separation of church and state given by John F. Kennedy - the nation’s first Catholic president - made him want to “throw up”: Catholic voters - representing nearly a third of the electorate - backed Romney, a Mormon, over Santorum, a devout Catholic, 44 to 37 percent.

And Santorum might be rethinking his decision to call President Obama a “snob” for wanting everyone to attend college: Voters who never attended college did break for Santorum, by a margin of 8 points. But they represented just 18 percent of the electorate. The 82 percent who attended college (including those without degrees) went for Romney over Santorum, 42 to 37 percent.

Romney still does better with higher-income voters, but is closing the gap somewhat: He beat Santorum among voters earning $100K a year or more by 14 points; he lost those earning $50-100K by just 3 points, and lost those earning less than $50K by 5 points.

And Romney still does much better with older voters: He won voters over 50 - and did especially well with the over-65 set, who went for Romney over Santorum by 49 to 33 percent. Santorum won voters between the ages of 30 and 50, while Ron Paul once again won among the 18 to 29 set.